1. Field of the Invention
The invention is related to the field of disk drive systems, and in particular, to disk drive systems and circuitry that use a zero forcing algorithm to produce the coefficients for the adaptive filter in the read channel.
2. Statement of the Problem
FIG. 1 depicts a conventional system that includes a host computer system 100 and a disk drive system 102. The disk drive system 102 includes control circuitry 104 and disk device 106. The disk device 106 stores data for the computer system 100. To transfer this data from the disk device 106 to the computer system 100, the disk device 106 transfers a signal 120 to the control circuitry 104. The signal 120 is an analog representation of the data. The control circuitry 104 converts the signal 120 into a signal 126 for the computer system 100. The signal 126 is a digital representation of the data and is suitable for processing by the computer system 100. Thus, the control circuitry 104 converts an analog representation of the data into a digital representation of the data.
Those skilled in the art will appreciate that numerous conventional components of the disk drive system 102 are not depicted on FIG. 1 for the purpose of clarity. For example, the disk device 106 typically includes disks on which data is written, heads to write/read the data to/from the disks, and motors that position heads and rotate the disks. The control circuitry 104 typically includes a controller, servo circuitry, and a read channel. The controller manages data transfers. The servo circuitry controls the motors to position the heads and rotate the disks. The read channel converts the analog signals from the disks into usable digital data. The read channel includes an adaptive filter 108, a Least Mean Square (LMS) circuit 110, and an adder 112 that are shown on FIG. 1.
The adaptive filter 108 is a digital Finite Impulse Response (FIR) filter that receives an input signal 121. The input signal 121 is a sampled version of the signal 120. The adaptive filter 108 processes the samples in the input signal 121 to generate the output signal 122. In particular, the adaptive filter 108 digitally alters pulses in the input signal 121 into a shape that is more suitable for processing by subsequent detector circuitry (not shown). The adaptive filter 108 continually improves its performance by adjusting internal coefficients in response to a coefficient signal 125. It should be appreciated that improving the performance of the adaptive filter 108 will reduce data errors in the signal 126.
The adder 112 receives a copy of the output signal 122 and an ideal signal 123. The ideal signal 123 can be generated in numerous ways, such as using a slicer on the output signal 122 or by using a digital copy of the data stored on the disk device 106. The adder 112 subtracts the output signal 122 from the ideal signal 123 to generate the error signal 124. The adder 112 provides the error signal 124 to the LMS circuit 110.
The LMS circuit 110 receives input signal 121 and the error signal 124. The LMS circuit 110 applies an LMS algorithm to produce the coefficient signal 125 that alters the coefficients in the adaptive filter 108. The LMS algorithm is:
CK+1=CK+xcexceKXK
where:
CK+1=the new coefficient signal 125
CK=the old coefficient signal 125
xcexc=the step size
eK=the error signal 124=iK(ideal signal 123)xe2x88x92yK(output signal i 22); and
XK=the input signal 121.
The upper case variables represent vectors that are comprised of scalar values that are represented by lower case variables. For a ten tap filter, the term eKXK can be represented by the following values: [eKxK, eKxKxe2x88x921, eKxKxe2x88x922, eKxKxe2x88x923, eKxKxe2x88x924, eKxKxe2x88x925, eKxKxe2x88x926, eKxKxe2x88x927, eKxKxe2x88x928, eKxxxe2x88x929]. A more economically efficient implementation replaces the term eKXK in the LMS algorithm with xKEK. For a ten tap filter, the term xKEK can be represented by the following values: [xKeK, xKeK+1, xKeK+2, xKeK+3, xKeK+4, xKeK+5, xKeK+6, xKeK+7, xKeK+8, xKeK+9].
Thus, the LMS circuit 110 improves the bit error rate performance of the disk drive system 102 by adjusting the coefficients in the adaptive filter 108. Unfortunately, the bit error rate performance of the conventional disk drive system 102 suffers because the adaptive filter coefficients do not converge to a solution for optimum bit error rate performance. The convergence problem is derived from the fact that LMS circuit 110 adjusts the coefficients using a Mean Squared Error (MSE) driven process. Although MSE is a convenient metric that correlates with bit error rate, the correlation is not perfect. Thus, the convergence problem in the conventional disk drive 102 permits additional data errors to remain that prevent or slow the operation of the computer system 100. The additional data errors also require more expensive disk drive components to compensate for the errors.
Given the enormous growth in the demand for higher capacity computer data storage, there is an acute need to continually improve the performance of disk drive systems. In particular, solutions are needed to reduce the problem of data errors in disk drive systems. These solutions will allow less expensive components to be used while maintaining or improving current error rates. The cost savings can be passed on to the consumer in the form of less expensive computer data storage.
The invention solves the above problem by using a zero forcing algorithm to adjust the coefficients in the adaptive filter. Testing has demonstrated that systems using the zero forcing algorithm have better bit error rate performance than conventional systems using the LMS algorithm. Thus, the invention allows the read channel adaptive filter to converge to a solution closer to the minimum bit error rate than does LMS circuitry using an MSE driven process. Consequently, the problem of data errors in disk drive systems is reduced, so less expensive disk drive components may be used while maintaining or improving current bit error rates.
The invention includes disk drive circuitry, systems, and methods. The disk drive system comprises control circuitry and a disk device. The disk device stores data and transfers an analog signal representing the data. The control circuitry receives the analog signal, converts the analog signal into a digital signal, and transfers the digital signal. The control circuitry includes zero forcing circuitry and an adaptive filter. The zero forcing circuitry produces new coefficients for the adaptive filter.
In some examples of the invention, the control circuitry includes an analog-to-digital converter, adaptive filter, detector, decoder, and both zero forcing circuitry and LMS circuitry. The analog-to-digital converter receives and samples the analog signal to generate a sampled signal. The adaptive filter shapes the sampled signal based on coefficients to produce an equalized signal. The detector detects binary data from the equalized signal, and the decoder decodes the binary data to generate the digital signal. Either the zero forcing circuitry or the LMS circuitry may be selected to produce the coefficient signal that adjusts the coefficients in the adaptive filter.